The CoolMolecules site is perfect for exploring periodic trends. Evidence for almost any trend can be found in the data, either by actually looking at the bond lengths and angles or simply by observing which elements light up when you search the database.

Suggested Activity #1

One way to use the website to teach periodic trends is to have students do some exploration of the database (probably using one of the abbreviated databases such as the "include metals" version) first. You can ask them to pay special attention to, or even record on a table, bond lengths or angles of molecules composed of a single period or row, and then discuss the trends they come up with in class or you can pick out specific molecules for them to look at if you want to restrict their exploration a little more. Having students make molecular origami models of some molecules makes the trends extremely obvious because they can set the molecules next to one another and easily compare size and shape.

We selected the halogen column and had the database display only the molecules with halogens in the center. Then we looked clicked view, and looked at all the molecules, recording a few representative bond lengths in the table we constructed.

You can easily see that the bonds get longer as you go down the periodic table (aka as the atoms get bigger.) Looking at the Hydrogen column shows this trend especially clearly as does the diagonal of F-F, Cl-Cl, Br-Br, and I-I bonds and the mean of collected bond lengths.

Suggested Activity #2

The other way to use the website for this topic is to teach the trends and then reinforce the concepts by having the students search the database for evidence that supports those trends. Again we suggest having students record their data in tables or make paper models of some molecules that will allow them to easily compare the molecular data.